Magnetic core and clamp



Oct. 25, 1949.

D.' 'HAL'VORSEN MAGNETIC CORE AND CLAMP Filed April 9, 1945 D/FfW HALVORSEA/ Straw;

Patented Oct. 25, i949 UNITED STATES PATENT OFFICE Drew Halvorsen,Westfield, N. J assignor to Federal Telephone and Radio Corporation, New

York, N. Y., a corporation of Delaware Application April 9, 1945, SerialNo. 587,236

This invention relates to an inductance device such as a transformer orreactor.

An object of the invention is to obtain an inductance device such as atransformer .or reactor which is simple in construction, of relativelyfew parts and easily assembled.

Another object of the invention is to provide an inductance device inwhich eddy-current losses are greatly reduced due to the particularclamping means I have devised for holding the laminations together.

A further object is to provide a transformer structure which as a resultof its assembly and clamping arrangement will be adapted in itsoperation to maintain more constant inductance or magnetic reluctancecharacteristics particular- 1y under the influence of temperaturechanges.

A further object of my invention is to produce a device which will havea closer tolerance in induction values resulting from its structuralform by accurately determining the air gap of the laminated core plateswhich are centrally divided with their outer legs in abutting relationand with their center legs fitting the opening in the coil with thespacing determined by the outer leg engagement.

The construction in brief comprises a magnetic core member composed oftwo similar E-shaped structures orlaminated sections having their legsin juxtaposition to provide two closed magnetic paths with a commoncentral path formed by the center legs which are slightly shortened toprovide an air gap, the spacing of which by maintaining. closedimensions is employed to determine the impedance value of the inductorcoil. The primary and secondary coils'are fitted to surround the centerlegs of the core members in a special form of U-shaped yoke and acooperating spring retaining member is employed herewith to retain theparts in assembled position.

The assembly further is designed to effect retaining of the laminatedcore structures with nonpressure restriction of the plates perpendicularto their faces thereby to avoid pressure variables under conditions oftemperature change such as to alter the reluctance characteristics. Moreconstant inductance values are thereby maintained as is important intuned circuit uses.

Other features and detailsnof construction will appear as thespecification proceeds.

In the accompanying drawing and the following description I haveillustrated and described in detail some preferred embodiments of myinvention.

Fig. 1 is a side view of a preferred form of my inductor coil ormagnetic core with the shortened 3 Claims- (Cl. 175356) 2 center legsshown in dotted lines in order to illustrate the air gap which isprovided;

Fig. 2 is a top View of the same device;

Fig. 3 is the bottom view of the same device;

Fig. 4 is an edge view of the same device, and

Fig. 5 is the sectional view taken in the line 55 of Fig. 4.

The preferred form of my invention consists of a transformer or reactorhaving a winding l which may comprise a primary and a secondary coilfitted around the shortened center legs 2 of the two similar E-shapedlaminated sections 3. The gap 4 formed by the shortened center legs isshown clearly in Figs. 1 and 5. It will be readily seen that byproviding the laminated sections having their legs in juxtaposition, twoclosed magnetic paths with a common center path are formed.

In order to retain the parts so far described in assembled position Ihave devised a special U- shaped yoke 5 and cooperating spring retainingmember or clip 6. This yoke is made from a single piece of flexiblemetal and may be stamped from a flat piece of metal. It is cut out toprovide slot 1 to permit the laminations to extend therethrough. Thespring retaining member or clip 6 is thin enough to be resilient and isnormally of arcuate form of a lesser radius than that assumed in itsassembled position. It may be made of thin sheet spring brass or bronzeand has raised portions 8 near its ends which form retaining or lockingmeans. As best shown in Fig. 5 these raised portions 8 are integrallyformed by deforming the metal at one side of a. transverse cut toprovide inwardly directed shoulders with outwardly inclined cammingwalls adapted to facilitate assembling.

In assembling the parts, the requisite number of E-shaped laminations 3are placed against each other and with another like group are placedaround the winding l with their legs in juxtaposition, the ends of theoutside legs having been carefully machined. The yoke 5 is then fittedtherearound, parts of the laminated sections extending through the slot1 and the spring clip 6 is then inserted, one end first going under anend wall of one of the slots and the other end then fitting under an endwall of the other slot. The raised parts or projections B of the springclip cooperate with the slots and serve to lock the clip and the yoketogether. When the parts are thus assembled the spring is slightly bowedin the center as shown at 9 and raised at III in Figs. 1 and 5 wherebypressure is applied along the center legs substantially at right anglesto the Surfaces forming the air gaps. The clamp comprising the yoke 5and the spring clip 6, while holding the laminations together andmaintaining the dimensions of the air gap, does not actually exercise aclamping action on the laminations at right angles to the plane of theirsurface. This reduces the eddy-current losses which arise if theadjacent surfaces of the laminated sections are in too intimate contact.

The described arrangement provides for effectively retaining of partswhile avoiding varying compression or pressure application to the corelaminations such as produced by prior art structures whereintransversely applied clamping pressures are applied or wherein the corelaminations are rigidly connected in a block as by riveting. As isreadily appreciated the latter introduce pressure variables between theplates, particularly under temperature changes, such as to alter thereluctance characteristics from the desired constant value. Inaccordance with present practice the outer surfaces of plates oflaminated sections may be coated with an insulating and protectivecoating such as an insulating lacquer of a character to benon-restrictive of the permissive expansion and contraction as referredto.

By my method of manufacturing the inductance element a tolerance of plusor minus can be maintained. It is my understanding that at the presenttime manufacturers do not attempt to manufacture similar inductanceelements having a tolerance closer than approximately 5% in inductancevalue. Any closer inductance values are obtained by adjustments duringtest periods.

While the embodiment of the present invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is:

1. An inductive element comprising a two part magnetic laminated corecomposed of a pair of multi-legged elements, the opposed outside legsbeing in juxtaposition and the opposed center legs separated by an airgap, providing two closed magnetic paths, a clamp for holding the twoparts of the core together, comprising a U-shaped yoke of fiat flexiblemetal, a rectangular slot in each end of said yoke to permit thelaminations to extend therethrough and a spring retaining membercooperating with said yoke, said yoke and spring being constructed andpositioned to provide a parallel relation of the clamp elements and themagnetic path of the core.

2. A magnetic core device comprising two sets of multi-leggedlaminations held together by a clamp comprising a U-shaped yoke of flatmetal, said yoke having a flat middle Prtion and two arms at rightangles to said middle portion, rectangular slots in said arms of saidyoke, a bowed shaped spring, raised portions integrally formed near theends of said spring, the upper horizontal sides of said slots beingabove the edges of said core and that portion of said arms above saidslots engaging said raised portions of said spring so as to lock saidspring and yoke when said spring is in position and to form a completemagnetic path parallel to the magnetic path of the core, saidlaminations extending through said slots so as to be held by said arms.

3. A magnetic core device comprising two sets of multi-Jeggedla-minations, said laminations having outside legs in juxtaposition andan opposed pair of center legs, an air gap separating said center legs,a clamp comprising a spring clip and a yoke, said clip having raised endportions and said yoke having rectangular slots formed so as to permitsaid end portions to pass through and lock said clip and yoke, thusforming a complete magnetic path parallel to the magnetic path of thecore, said clip having a bowed section contacting the outer edges ofsaid laminations over the center pair of opposed legs whereby pressureis applied to said set of laminations so as to maintain the dimensionsof said air gap, said laminations being formed so as to extend throughsaid slots and be retained therein.

DREW HALVORSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 708,132 Fleming Sept. 2, 19021,539,928 Angus June 2, 1925 1,579,955 Schermerhorn et a1. Apr. 6, 19261,974,588 Snell Sept. 25, 1934 2,068,320 Grant Jan. 19, 1937 2,229,373Cole Jan. 21, 1941 2,261,323 Zierdt Nov. 4, 1941 2,317,844 Boucher Apr.27, 1943 2,367,591 McAllister Jan. 16, 1945 2,372,067 Forbes Mar. 20,1945 FOREIGN PATENTS Number Country Date 388,803 Great Britain Feb. 28,1933

